本文主要是介绍mybatis mysql 方言_iBatis3基于方言(Dialect)的分页，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
(注:以下代码是基于ibatis3 beta4的扩展，ibatis3正式版如果实现改变，将会继续跟进修改)
iBatis3默认使用的分页是基于游标的分页，而这种分页在不同的数据库上性能差异不一致，最好的办法当然是使用类似hibernate的基于方言(Dialect)的物理分页功能。
iBatis3现在提供插件功能，通过插件我们可以编写自己的拦截器来拦截iBatis3的主要执行方法来完成相关功能的扩展。
能够拦截的的类如下:
Java代码
Executor
(update,query,flushStatements,commit,rollback,getTransaction,close,isClosed)
ParameterHandler
(getParameterObject,setParameters)
ResultSetHandler
(handleResultSets,handleOutputParameters)
StatementHandler
(prepare,parameterize,batch,update,query)
但此次我们感兴趣的是Executor.query()方法，查询方法最终都是执行该方法。
该方法完整是:
Java代码
Executor.query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;
分页方言的基本实现:
以Mysql数据库示例,即有一个方法 query(sql,offset,limit);
Java代码
query("select * from user",5,10);
经过我们的拦截器拦截处理,变成
Java代码
query("select * from user limit 5,10",,);
1.拦截类实现:
Java代码
@Intercepts({@Signature(
type= Executor.class,
method = "query",
args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class OffsetLimitInterceptor implements Interceptor{
static int MAPPED_STATEMENT_INDEX = ;
static int PARAMETER_INDEX = 1;
static int ROWBOUNDS_INDEX = 2;
static int RESULT_HANDLER_INDEX = 3;
Dialect dialect;
public Object intercept(Invocation invocation) throws Throwable {
processIntercept(invocation.getArgs());
return invocation.proceed();
}
void processIntercept(final Object[] queryArgs) {
//queryArgs = query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler)
MappedStatement ms = (MappedStatement)queryArgs[MAPPED_STATEMENT_INDEX];
Object parameter = queryArgs[PARAMETER_INDEX];
final RowBounds rowBounds = (RowBounds)queryArgs[ROWBOUNDS_INDEX];
int offset = rowBounds.getOffset();
int limit = rowBounds.getLimit();
if(dialect.supportsLimit() && (offset != RowBounds.NO_ROW_OFFSET || limit != RowBounds.NO_ROW_LIMIT)) {
BoundSql boundSql = ms.getBoundSql(parameter);
String sql = boundSql.getSql().trim();
if (dialect.supportsLimitOffset()) {
sql = dialect.getLimitString(sql, offset, limit);
offset = RowBounds.NO_ROW_OFFSET;
} else {
sql = dialect.getLimitString(sql, , limit);
}
limit = RowBounds.NO_ROW_LIMIT;
queryArgs[ROWBOUNDS_INDEX] = new RowBounds(offset,limit);
BoundSql newBoundSql = new BoundSql(sql, boundSql.getParameterMappings(), boundSql.getParameterObject());
MappedStatement newMs = copyFromMappedStatement(ms, new BoundSqlSqlSource(newBoundSql));
queryArgs[MAPPED_STATEMENT_INDEX] = newMs;
}
}
private MappedStatement copyFromMappedStatement(MappedStatement ms,SqlSource newSqlSource) {
Builder builder = new MappedStatement.Builder(ms.getConfiguration(),ms.getId(),newSqlSource,ms.getSqlCommandType());
builder.resource(ms.getResource());
builder.fetchSize(ms.getFetchSize());
builder.statementType(ms.getStatementType());
builder.keyGenerator(ms.getKeyGenerator());
builder.keyProperty(ms.getKeyProperty());
builder.timeout(ms.getTimeout());
builder.parameterMap(ms.getParameterMap());
builder.resultMaps(ms.getResultMaps());
builder.cache(ms.getCache());
MappedStatement newMs = builder.build();
return newMs;
}
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}
public void setProperties(Properties properties) {
String dialectClass = new PropertiesHelper(properties).getRequiredString("dialectClass");
try {
dialect = (Dialect)Class.forName(dialectClass).newInstance();
} catch (Exception e) {
throw new RuntimeException("cannot create dialect instance by dialectClass:"+dialectClass,e);
}
System.out.println(OffsetLimitInterceptor.class.getSimpleName()+".dialect="+dialectClass);
}
public static class BoundSqlSqlSource implements SqlSource {
BoundSql boundSql;
public BoundSqlSqlSource(BoundSql boundSql) {
this.boundSql = boundSql;
}
public BoundSql getBoundSql(Object parameterObject) {
return boundSql;
}
}
}
2.ibatis3配置文件内容:
Xml代码
3.MysqlDialect实现
Java代码
public class MySQLDialect extends Dialect{
public boolean supportsLimitOffset(){
return true;
}
public boolean supportsLimit() {
return true;
}
public String getLimitString(String sql, int offset, int limit) {
return getLimitString(sql,offset,String.valueOf(offset),limit,String.valueOf(limit));
}
public String getLimitString(String sql, int offset,String offsetPlaceholder, int limit, String limitPlaceholder) {
if (offset > ) {
return sql + " limit "+offsetPlaceholder+","+limitPlaceholder;
} else {
return sql + " limit "+limitPlaceholder;
}
}
}
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